The present invention relates generally to tractor hydraulic systems and, more particularly, to a modulation control system for the hydraulic clutch controlling operation of the tractor power-takeoff shaft.
Tractors are typically provided with a power-takeoff shaft operably rotated by the engine carried by the tractor to provide a source of rotational power to an implement or device connected to the tractor. In some instances, the implement connected to the tractor power-takeoff shaft contains considerable mass resulting in a high inertia load to overcome before effecting operation thereof. The on/off control of the tractor PTO is often accomplished through a hydraulic clutch which when engaged permits the transfer of rotational power from the engine to the power-takeoff shaft to operably drive the implement attached thereto.
An instantaneous loading or engagement of the hydraulic clutch in instances where the implement attached to the power-takeoff shaft has a high inertia load can result in structural damage to various components, such as shear bolts typically provided in the implement drive line to protect both the implement and the tractor power-takeoff shaft from shock loading.
Accordingly, it would be desirable to gradually increase the hydraulic pressure applied to the hydraulic clutch for engagement of the power-takeoff shaft in a smooth manner. Prior art devices to accomplish this objective have included mechanical devices, including springs and linkages, to restrict the movement of the valve spool or other structure inhibiting the full engagement of the power-takeoff shaft. Another approach is to utilize electronics, such as through pulse width modulation to modulate the increase in hydraulic pressure to the hydraulic clutch and, therefore, enable a gradual overtaking of the inertia load associated with the attached implement. It would be desirable, however, to provide a simpler, less costly approach to effect a modulation of the hydraulic pressure applied to the PTO clutch.